The present invention relates to a static electrical induction apparatus such as transformers, reactors or the like and in particular to a winding structure for such induction apparatus which is provided with a cooling arrangement.
There is hitherto known such a winding structure for the static electrical induction apparatus in which an annular winding assembly constituted by a plurality of vertically stacked coil units is disposed in an annular space defined between an inner insulation cylinder and an outer insulation cylinder so as to define an inner and an outer paths to allow coolant in aqueous or liquid phase to flow in the vertical direction by natural circulation. Such paths are referred to hereinafter as vertical cooling or coolant passages. Further, the coil units are spaced from one another to define between the adjacent ones of the horizontal cooling passages which are communicated with the inner and the outer vertical cooling passages. With such arrangement of the cooling passages only, the flow of the coolant in the cooling passages is too gentle to attain a desired cooling effect for the winding assembly. This is particularly true for the case where the coolant is to flow under natural circulation. With attempt to delete this disadvantage in the apparatus of the natural circulation type, there has been proposed to divide each of the coil units constituting the winding assembly into two conventional sub-units thereby to define an intermediate vertical passage extending vertically in the axial direction of the winding assembly between the inner and the outer coil sub-units. Such intermediate vertical cooling passage is certainly effective for lowering the temperature at the mid portion of the coil units. However, the coolant flow in the horizontal passages remains still at a low level so that the temperature at middle portions of the divided coil sub-units will be locally increased. Of course, the number of the intermediate vertical passages may be increased through corresponding divisions of the disk-like coil units. However, this involves correspondingly enlarged width of the coil-units and hence of the winding assembly, which means anything but an increased dimension or bulkiness of the static electrical induction apparatus for a given capacity.
In the apparatus of the forced cooling type, on the contrary, there has been proposed to divide the whole cooling region into several sections in each of which a flow deflector or baffle plate is provided thereby to cause coolant flow in a zig-zag flow pattern for every cooling region. However, such attempts have not led to satisfactory results. The coil units constituting the winding assembly can not be cooled uniformly and there arises a danger of local abnormal temperature rise occurring in the respective cooling regions which may eventually degrade the used insulation material of the winding assembly and thus reduce the use life of the induction apparatus.
In an effort to evade the difficulties in the cooling of the winding assembly, the induction apparatus is used at a low current density in the individual conductors constituting the winding, or the winding assembly is designed and manufactured so as to prevent the unwanted local temperature rise from occurring even at the regions where the most slow flow of the coolant is likely to take place. Such measures will apparently involve a remarkably increased dimension or bulkiness of the winding assembly and the induction apparatus for a given capacity.
It is also known to increase the number of the deflector plate for causing the coolant flow in the zig-zag pattern or provide additionally flow adjusting members having a similar function as the deflector plate in an effort to attain a coolant flow as uniformly as possible. Such arrangements however suffer from drawbacks that the fluid pressure loss of the current is considerably increased and, additionally, the arrangement of the coolant passages becomes very complicated thereby making it difficult to obtain a compatibility of the winding assembly with the adjacent other winding such as cylindrical winding in respect of the distribution of the coolant flows.